The present invention relates to methods for transmitting and receiving audio/visual data. More specifically, the invention relates to methods for a video conference system to transmit and receive audio/visual data during periods of reduced bandwidth.
The present invention relates to an improved method for transmitting audio/visual data particularly for video conference systems. Video conference systems are becoming increasingly important for long distance communication. With the use of a video conference system participants can see and talk to each other over a system of two or more individual units each consisting of a viewing device, a speaker, a microphone, and a video camera. The signals are transmitted over a communications means such as telephone lines, cable, satellite etc. with many current video conference systems utilizing the internet for transmission of the video and audio data. The International Telecommunications Union (ITU) has established the H.323 standard (version 2, dated January 1998) for computers, equipment, and services for multimedia communications over networks allowing users to connect over the internet using different products that support H.323. H.323 systems can carry real-time video, audio, and data, or any combination of these elements. The H.323 standard defines how the audio and video information is formatted and packaged for transmission over the network. Standard audio and video codecs encode and decode input/output analog data from the audio and visual sources into digital data for transmission over the communication means.
A significant difficulty in transmitting audio and especially video is a lack of bandwidth, and problems with latency. Bandwidth is the measurement of the capacity to deliver information in bits per second and is crucial when precise amounts of information must be provided within a certain amount of time. Bandwidth problems can be caused by the equipment, media, and the internet infrastructure. In a video conference application where the flows of audio and video data are constant it is crucial that the system has enough bandwidth for transmitting the data. For example digitized phone-quality speech (8-bit sample, 8000 samples per second) requires approx. 64 Kbps of data. Full motion video for a 1024xc3x97768 pixel display, with 3 colors at 8 bits each, displayed at 30 frames per second, equates to approx. 566,000 Kbps of throughput. In a conventional system when the transmission bandwidth lowers during transmission, the system will drop video frames, to maintain the video stream over the new lower bandwidth. This method though is very problematic though, as the received video appears very jerky. Therefore a need exists for sending audio-video data during a drop in available bandwidth during transmission without substantially affecting the video quality.
It is an object of the invention to provide a method for improving the visual and audio signals transferred during a reduced bandwidth period. A video conference system transfers audio and visual data over a communications means which in a preferred embodiment is the internet. When the available bandwidth drops during the transfer of data (when a conference is in progress) the video conference system will start transmitting and receiving data in a QCIF format rather than a CIF format to prevent the dropping of frames, while maintaining video continuity and quality. The video conference units will receive the visual data in the QCIF format and rescale it back into a CIF format for viewing. In another embodiment of the invention if the bandwidth drops the audio format can be changed according to the amount of bandwidth available. In yet another embodiment of the invention a user can select preferences and according to the methods shown by the invention the audio quality can be reduced while preserving video quality, or opposingly video can be sent in a QCIF format in order to preserve audio quality.
These and other features, which characterize the invention, are set forth in the claims annexed hereto and forming a further part hereof. However, for a better understanding of the invention, and of the advantages and objectives attained through its use, reference should be made to the drawings, and to the accompanying descriptive matter, in which there is described exemplary embodiments of the invention.